RecentSELEXResultsonthePropertiesofCharmedHadrons · 4 6 8 10 12 14 0 50 100 150 200 250 300 Momentum [GeV/c] Radius [cm] SELEX RICH 53229793 Single negative track events Omega Xi

Recent SELEX Results on the Properties of Charmed Hadrons

Jurgen Engelfried, Instituto de Fısica, Universidad Autonoma de San Luis Potosı, Mexico

For the SELEX (Fermilab E781) Collaboration

Outline• Introduction

• The SELEX Experiment

• Double-Charm Baryons

• Ds(2632)

• Summary and Outlook

[email protected], http://www.ifisica.uaslp.mx/˜jurgen

Introduction

• Mesons consist of 2 valence quarks

• Baryons consist of 3 valence quarks

• 4, 5, and 6 quark systems not yet

unambiguously confirmed

• there are 6 different types of quarks

• only 5 of them form hadrons.

• A lot of possible baryons states

• All ground states, first excited states

with one charm quark observed:

Mesons: D0 (cu), D+ (cd), D+s (cs), Ψ

Baryons (cqq): Λ+c , Σ0c, Σ

+c , Σ

++c

Baryons (csq): Ξ0c, Ξ+c , Ξ

′0c , Ξ

′+c

Baryon (css): Ω0c

Recent SELEX results on the properties of charmed hadrons Jurgen@QC2004 22Sep2004. 2

Model Predictions for Doubly Charmed Baryon Masses

author year model Ξcc(J = 3/2) Ξcc(J = 1/2)

Bjorken 1986 phenom 3.70GeV/c2 3.64GeV/c2

Fleck & Richard 1989 bag 3.636 3.516

Fleck & Richard 1989 quarkonium 3.741 3.613

Roncaglia et al. 1995 Feynmann/Hellman 3.81 3.66

Ellis 2002 phenom 3.711 3.651

• ground states near 3.6GeV/c2

• ground states Isospin=1/2 multiplets

degenerate

• Hyperfine splitting around

60− 120MeV/c2

• Most predict electromagnetic hyper-

fine transition (but some pionic)

• Model dependent predictions for or-

bital and radial excitations

• Some Models: Light Quark excitation

characteristics similar to heavy-light

meson spectra (heavy (cc) diquark)

Production

• Basically no models

(except independent production)

• Expect small production cross section

• But why not look anyway??


The SELEX (Fermilab E781) Collaboration

G.P. Thomas

Ball State University, Muncie, IN 47306, U.S.A.

E. Gulmez

Bogazici University, Bebek 80815 Istanbul, Turkey

R. Edelstein, S.Y. Jun, A.I. Kulyavtsev1, A. Kushnirenko2,

D. Mao3, P. Mathew4, M. Mattson, M. Procario5, J. Russ, J. You1

Carnegie-Mellon University, Pittsburgh, PA 15213, U.S.A.

A.M.F. Endler

Centro Brasileiro de Pesquisas Fısicas, Rio de Janeiro, Brazil

P.S. Cooper, J. Kilmer, S. Kwan, J. Lach, E. Ramberg, D. Skow,

L. Stutte

Fermi National Accelerator Laboratory, Batavia, IL 60510, U.S.A.

V.P. Kubarovsky, V.F. Kurshetsov, A.P. Kozhevnikov,

L.G. Landsberg, V.V. Molchanov, S.B. Nurushev, S.V. Petrenko,

A.N. Vasiliev, D.V. Vavilov, V.A. Victorov

Institute for High Energy Physics, Protvino, Russia

Li Yunshan, Mao Chensheng, Zhao Wenheng, He Kangling,

Zheng Shuchen, Mao Zhenlin

Institute of High Energy Physics, Beijing, P.R. China

M.Y. Balatz6, G.V. Davidenko, A.G. Dolgolenko,

G.B. Dzyubenko, A.V. Evdokimov, M.A. Kubantsev, I. Larin,

V. Matveev, A.P. Nilov, V.A. Prutskoi, A.I. Sitnikov,

V.S. Verebryusov, V.E. Vishnyakov

Institute of Theoretical and Experimental Physics, Moscow,

Russia

U. Dersch7, I. Eschrich8, I. Konorov9, H. Kruger10, J. Simon11,

K. Vorwalter12

Max-Planck-Institut fur Kernphysik, 69117 Heidelberg, Germany

I.S. Filimonov6, E.M. Leikin, A.V. Nemitkin, V.I. Rud

Moscow State University, Moscow, Russia

A.G. Atamantchouk6, G. Alkhazov, N.F. Bondar, V.L. Golovtsov,

V.T. Kim, L.M. Kochenda, A.G. Krivshich, N.P. Kuropatkin1,

V.P. Maleev, P.V. Neoustroev, B.V. Razmyslovich13,

V. Stepanov13, M. Svoiski13, N.K. Terentyev14, L.N. Uvarov,

A.A. Vorobyov

Petersburg Nuclear Physics Institute, St. Petersburg, Russia

I. Giller, M.A. Moinester, A. Ocherashvili15, V. Steiner

Tel Aviv University, 69978 Ramat Aviv, Israel

J. Amaro-Reyes, A. Blanco C., J. Engelfried1, A. Morelos,

I. Torres, E. Vazquez-Jauregui

Universidad Autonoma de San Luis Potosı, San Luis Potosı,

Mexico

M. Luksys

Universidade Federal da Paraıba, Paraıba, Brazil

V.J. Smith

University of Bristol, Bristol BS8 1TL, United Kingdom

U. Akgun, A.S. Ayan, M. Kaya16, E. McCliment, K.D. Nelson17,

C. Newsom, Y. Onel, E. Ozel, S. Ozkorucuklu18, P. Pogodin

University of Iowa, Iowa City, IA 52242, U.S.A.

L.J. Dauwe

University of Michigan-Flint, Flint, MI 48502, U.S.A.

M. Gaspero, M. Iori

University of Rome “La Sapienza” and INFN, Rome, Italy

L. Emediato, C.O. Escobar19, F.G. Garcia1, P. Gouffon,

T. Lungov, M. Srivastava, R. Zukanovich-Funchal

University of Sao Paulo, Sao Paulo, Brazil

A. Lamberto, A. Penzo, G.F. Rappazzo, P. Schiavon

University of Trieste and INFN, Trieste, Italy


The SELEX Experiment at Fermilab

Elevator

W

E

S N

G as

H ouse

H yperon Targetting

M agnet Photon 2

Target,

V ertex

region

M 1

Photon 1

D C

PW C

BTRD

M 2

PW C

HOD1

eTRD Ring-Im aging Cherenkov

neutron

calorim eter

Photon3M 3

PC3 PC4

V ee A V ee B V ee C

.

PW C

0 m 20 m 40 m 50 m

HOD2

10 m 30 m 60 m

Selex (E781)Proton Center Layout

20 µm pitch VX Si detectors

25 µm pitch VX Si detectors

u y x

20 µm pitch Beam Si detectors

TargetsCu Diamond

InteractionScintillators

0 20-20 40 Z [cm]

-2

0

+2

X [cm]

Vertex RegionS4 Beam Scintillator

Interaction Veto (V5) Scintillator

30 50-10 10

x y 1 u v x y 2 u v

x y 3 u v x y 4 u v x v 5 u x

SELEX experiment

• Forward (xF > 0.1)

charm production

• Σ−, π, p beam at

600GeV/c

• RICH PID above

∼ 22GeV/c

• 20 plane Si-Vertex.

• Data taken 1996/7Recent SELEX results on the properties of charmed hadrons Jurgen@QC2004 22Sep2004. 5

Vertex Spectrometer Performance

Primary and Secondary Vertex ResolutionPrimary and Secondary Vertex Resolutioncm

even

ts

Primary

Secondary

Primary vertex positionscm

even

ts

Primary vertex positions

0

2000

4000

6000

8000

10000

12000

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

0

500

1000

1500

2000

2500

3000

-7 -6 -5 -4 -3 -2 -1 0 1

• transverse vtx resolution

8− 15µm

• 20 highly-efficient vertex

planes over-determine tracks,

reduce tracking confusion in

high-multiplicity events

• target foils 0.8-2.2 mm thick

with 1.5 cm spacing to localize

primary interaction

• Lifetime resolution ∼ 20 fs

(slightly depending on particle

and decay mode)


Ring Imaging Cherenkov Counter Performance

0

2

4

6

8

10

12

14

0 50 100 150 200 250 300

Momentum [GeV/c]

Rad

ius

[cm

]

SELEX RICH 53229793 Single negative track events

Omega

Xi

Sigma

Proton

Kaon

Pion

Muon

SELEX RICH Group, J. Engelfried, June 2002

0

0.2

0.4

0.6

0.8

1

1.2

0 50 100 150 200 250 300 350 400 450 500Proton momentum [GeV/c]

Pro

ton

eff

icie

ncy

0

500

1000

1500

2000

2500

3000

1 1.025 1.05 1.075

M(K+K-), [GeV/c2]

N /

1 M

eV/c

2

4346±225 φ

0

200

400

600

800

1000

1 1.025 1.05 1.075

M(K+K-), [GeV/c2]

N /

1 M

eV/c

2

4206±126 φ

0

100

200

300

400

500

600

700

1 1.025 1.05 1.075

M(K+K-), [GeV/c2]

N /

1 M

eV/c

2

3896±96 φ

0

0.2

0.4

0.6

0.8

1

50 100 150

P(K), [GeV/c]

Eff

icie

ncy


Selex publications

1. Observation of the Cabibbo-suppressed decayΞ+

c → pK−π+. Phys. Rev. Letter 84 (2000) 1857-1861.

2. Total Cross Section Measurements with π−, Σ−

and Protons on Nuclei and Nucleons around600GeV/c. Nucl. Phys. B 579 (2000) 277-312.

3. Measurement of the Σ− Charge Radius by Σ−–Electron Elastic Scattering. Physics Letters B522(2001) 233-239.

4. Precision measurements of the Λ+c and D0 life-

times. Phys. Rev. Letter 86 (2001) 5243-5246.

5. Radiative decay width of the a2(1320)− meson.

Physics Letters B521 (2001) 171-180.

6. Measurement of the Ds lifetime. Physics Let-ters B523 (2001) 22-28.

7. Hadronic Production of Λc from 600GeV/c π−,Σ− and p beams. Physics Letters B528 (2002),49-57.

8. First Measurement of π−e → π−eγ Pion VirtualCompton Scattering. Phys. Rev. C 66, 034613(2002).

9. First Observation of the Doubly Charmed BaryonΞ+

cc. Phys. Rev. Letters 89 112001 (2002).

10. Production Asymmetry for Ds for 600GeV/cΣ− and π− beam. Physics Letters B558 (2003)34-40.

11. Upper limit on the decay Σ(1385)− → Σ−γ andcross section for γΣ− → Λπ−. Physics LettersB590, 161-169 (2004).

12. Polarization of Σ+ Hyperons produced by 800GeV/cProtons on Cu and Be. Submitted to PRD.

13. Confirmation of the Double Charm Baryon Ξ+cc

via its Decay to pD+K−. Submitted to PRL,hep-ex/0406033.

14. First Observation of a Narrow Charm-StrangeMeson D+

sJ → D+s η and D0K+. Submitted to

PRL, hep-ex/0406045.

Charm Topics Non-Charm Topics


SELEX Single Charm Analysis

~©©¼

Target region

~

****

****

****

****

****

****

¾ L -

¢¢¢¢¢¢¢

HHHHj

¡¡¡¡µ

π+

p

K−

¼¼¼¼¼¼¼ p

σs

σp

b

-Beam

Charm Analysis Cuts

• Decay vertex separation significance

L/σ

• Charm vector momentum points back

to primary: cut on (b/σb)2 (point-back

cut)

• Decay vertex lies outside target

material (space cut)

• Proton and Kaon identified in RICH

detector• Λ+c → pK−π+ sample used to search

for double charm


SELEX Charm Selection Criteria

20 µm pitch Si detectors


u y x


TargetsCu Diamond

InteractionScintillators

0 20-20 40 Z [cm]

-2

0

+2

X [cm]

Beam Scintillator

Interaction Veto Scintillator

30 50-10 10

x y 1 u v x y 2 u v

x y 3 u v x y 4 u v x v 5 u x

P[GeV/c] 381 M = 2287(5) MeV/c2

153 L = 2.245(56) cm 154 Lmin= 0.445 cm [ 8σ]

7 4 τ = [L-Lmin]M/Pc

= 359(11) fsec

~ 1.8 τ[ Λc+]

π+p

K-

Λc+

0 1 2 3Z [cm]

0.00

0.01

0.02

-0.01

X [cm]

L

Lmin

Λ+c event

• primary vertex tagged by beam track

• secondary vertex must lie outside material

Charm Selection Cuts for

single charm studies:

• secondary vertex significance:

– L/σ ≥ 1 short-lived states

(Ξ0c, Ω0c)

– L/σ ≥ 8 long-lived states

(Λ+c , D+)

• Pointback ≤ 4 (2σb)

• second-largest miss significance

among decay tracks ≥ 4.


SELEX Search Strategy for Doubly-Charmed Baryons

Vertex

K-

K-

ccd

Track

1L L2

p

+

Ξ +cc

cΛVertex

Decay Schematic

π+

π+

Beam

PrimaryVertex

• ccq decays to csqud. Look for charm,

strange and baryon in final state.

SELEX started with Λ+cK−π+(π+).

• Look for new secondary vertex

between primary and Λ+c

• no RICH PID on new K−π+ tracks (too

soft)

• All other cuts fixed from previous searches


SELEX: Experimental Evidence from 2002

SELEX reported 3 significant high mass peaks

• in Λ+cK−π+ at 3520MeV/c2

• in Λ+cK−π+π+ at 3460MeV/c2 and 3780MeV/c2

0

1

2

3

4

5

6

7

8

3.46 3.48 3.5 3.52 3.54 3.56 3.58

Λ+

c K- π+

M(Λ+c K

- π+) GeV/c2

Eve

nts

/2.5

MeV

/c2

Mass 3520 MeV/c2

Sigma 3 MeV/c2

signal/√(back)

16/√(6) = 6.5σ

Signal Channel

Wrong-Sign

Poisson Prob < 10-6

M(Λ+c K

- π+) GeV/c2

Eve

nts

/2.5

MeV

/c2

0

0.5

1

1.5

2

2.5

3

3.5

4

3.3 3.35 3.4 3.45 3.5 3.55 3.6

Λ+

c K- π+ π+

RIGHT-SIGN cos(θK*) > -.6

WRONG-SIGN cos(θK*) > -.6

0

2

4

6

8

10

12

3.4 3.5 3.6 3.7 3.8 3.9 4

Λ+

c K- π+ π+Mean 3780 MeV/c2

Sigma 26 MeV/c2

signal/√(back)31/√(31) = 5.6σ

Data

SELEX argued that these states are doubly-charmed baryons

First Observation of the Doubly Charmed Baryon Ξ+cc → Λ+

c K−π+. Phys. Rev. Letters 89 (2002) 112002.


SELEX: Search for ccd+(3520) Isopartner: ccu++

• same cuts as before:

3.5σ hint in Λ+cK−π+π+.

• No peak in wrong sign (Λ+cK+π−π+).

• Try additional cut: cosΘ∗K > −0.6 to

remove soft vertex tracks

• Mass peak at 3460MeV/c2

7.1 signal, 0.9 background. 7.5σ

• Loss of signal consistent with phase space

(L = 0)

• Ξ++cc (3460), Ξ+cc(3520) Isodoublet??

0

0.5

1

1.5

2

2.5

3

3.3 3.35 3.4 3.45 3.5 3.55 3.6

Mass 3460 MeV/c2 Λ+

c K- π+ π+

Data

Wrong-sign events

signal/bkg

6.6/3.4

Poisson Prob

< .0027

M(Λ+c K

- π+ π+) GeV/c2

Even

ts/5

MeV

/c2

0

0.25

0.5

0.75

1

1.25

1.5

1.75

2

2.25

3.3 3.35 3.4 3.45 3.5 3.55 3.6


c K- π+ π+


signal/√(back)

7.1/√(.9) = 7.5σ

Poisson Prob

< 10-5

M(Λ+c K

- π+ π+) GeV/c2

Even

ts/5

MeV

/c2


SELEX: Where is the Isopartner to Ξ++cc (3460)?

• apply cosΘ∗K > −0.6 also to Λ+cK−π+

• ccd+(3520) strongly attenuated:

⇒ not phase space

•⇒ NOT isopartner to ccu++(3460)

New ccd+(3443) now very significant

• there was a “bump” before –

– was ignored

• Now: 7.4 signal, 1.6 background. 5.8σ

• Consistent with phase space decay

• ccd+(3443) is partner to ccu++(3460)

0

0.5

1

1.5

2

2.5

3

3.5

4

3.3 3.325 3.35 3.375 3.4 3.425 3.45 3.475 3.5


c K- π+

Data cosθ*

K>-.6

sig/bkg 7.4/1.6

Poisson Prob < 3.8 x 10-5

L/σ >1

M(Λ+c K

- π+) GeV/c2

Eve

nts

/2.5

MeV

/c2


SELEX: Where is the Isopartner to Ξ+cc(3520)?

• ccd+(3520) not phase space (cosΘ∗K cut)

• Λ+c and K− are back-to-back:

cosΘ∗K cosΘ∗Λc< −0.25 keeps most of sig-

nal

• Apply also to Λ+cK−π+π+ sample: Noth-

ing

• Reduce cut to L/σ > 0.25

New ccu++(3541) now very significant

• 7.4 signal, 1.6 background. 5.8σ

• Consistent with L > 0

• ccu++(3541) is partner to ccd+(3520)

0

0.5

1

1.5

2

2.5

3

3.3 3.35 3.4 3.45 3.5 3.55 3.6

Λ+

c K- π+ π+Mass 3541 MeV/c2

Data

Wrong-sign events

L/σ > .25

cosθK*cosθΛ < -.25

Poisson Prob< 5 x 10-5

signal/bkg

7.4/1.6

M(Λ+c K

- π+ π+) GeV/c2

Eve

nts

/5 M

eV/c

2


SELEX Double Charmed Baryon States

0

1

2

3

4

5

6

7

8

3.3 3.35 3.4 3.45 3.5 3.55 3.6

remove slow pion from Λ+

c K- π+ π+

peak at 3520 MeV/c2

sig/bkg 9.6/3.4

Prob. < 5.3 x 10-6

Lo sideband

Hi sideband2

Even

ts/1

0 M

eV/c

2

0

2

4

6

8

10

12

3.3 3.35 3.4 3.45 3.5 3.55 3.6

Λ+

c K- π+

Mass 3520 MeV/c2

Sigma 3 MeV/c2

signal/√(back)16/√(6) = 6.5σPoisson Prob < 10-6

0

0.5

1

1.5

2

2.5

3

3.5

4

3.3 3.35 3.4 3.45 3.5 3.55 3.6


c K- π+

Data cosθ*

K>-.6

sig/bkg 7.4/1.6

Poisson Prob

< 3.8 x 10-5

L/σ >1

An exited state and a pair of

isodoublets?

3400

3500

3600

3700

3800Λ

+

cK-π+ Λ

+

cK-π+π+

3780 MeV (1/2-)

3520 MeV3541 MeV L>0

(1/2-)21 MeV

3443 MeV3460 MeV L=0

(1/2+)17 MeV

π+260 MeV

78MeV

337MeV

0

2

4

6

8

10

12

3.4 3.5 3.6 3.7 3.8 3.9 4

Λ+

c K- π+ π+

peak: 3780 MeV/c2

sig/bkg 31/31

Ev/b

in

0

0.5

1

1.5

2

2.5

3

3.3 3.35 3.4 3.45 3.5 3.55 3.6

Λ+

c K- π+ π+Mass 3541 MeV/c2

Data L/σ > .25

cosθK*cosθΛ < -.25

Poisson Prob< 5 x 10-5

signal/bkg

7.4/1.6

0

0.25

0.5

0.75

1

1.25

1.5

1.75

2

2.25

3.3 3.35 3.4 3.45 3.5 3.55 3.6


c K- π+ π+


signal/√(back)

7.1/√(.9) = 7.5σ

Poisson Prob

< 10-5


Other Double Charm Baryon Decay Modes?New SELEX result on Ξ+cc → pD+K−: hep-ex/0406033, submitted to PRL

0

50

100

150

200

250

300

350

400

1.78 1.8 1.82 1.84 1.86 1.88 1.9 1.92 1.94 1.96

1450 D+

M(K- π+ π+)

Eve

nts

/5 M

eV/c

2

0

100

200

300

400

500

600

1.78 1.8 1.82 1.84 1.86 1.88 1.9 1.92 1.94 1.96

2450 D-

M(K+ π- π-)

Eve

nts

/5 M

eV/c

2

SELEX D+ and D−

Sample

0

0.5

1

1.5

2

2.5

3

3.5

4

3.46 3.48 3.5 3.52 3.54 3.56 3.58

(a) p D+ K-

peak mass:

3516 MeV

4-bin Poisson Prob

< 2.3 x 10-4

L/σ > 1.0

M(p D+ K-)

Eve

nts

/2.5

MeV

/c2

0

0.25

0.5

0.75

1

1.25

1.5

1.75

2

3.46 3.48 3.5 3.52 3.54 3.56 3.58

(b) wrong sign: p D- K-

L/σ > 1.0

M(p D- K-)

Sca

led

Eve

nts

/2.5

MeV

/c2


Both Ξ+cc Decay Modes combined

0

1

2

3

4

5

6

7

8

3.46 3.48 3.5 3.52 3.54 3.56 3.58

Λ+

c K- π+ and D+ p K-

fitted masses: 3519(2) and 3518(3)

MeV/c2

M(ccd)

Eve

nts

/2.5

MeV

/c2

Ξ+cc → Λ+cK−π+ : (3519± 2)MeV/c2

Ξ+cc → pD+K− : (3518± 3)MeV/c2

Γ(Ξ+cc → Λ+

c K−π+)

Γ(Ξ+cc → pD+K−)

= 0.078± 0.045

Not possible to access ccd(3443), ccu(3460), ccu(3541) with D modesRecent SELEX results on the properties of charmed hadrons Jurgen@QC2004 22Sep2004. 18

Doubly Charmed Baryons Properties

Lifetimes

• SELEX tried to measure lifetime: All lifetimes near resolution limit: τcc < 30 fs

• Decays are via weak interaction

• Model predictions: several hundreds of fs.

Production

• SELEX: Dominantly produced by baryon (Σ−, p) beam

• E791 has looked in 250GeV/c π− production no signal

• FOCUS looked in 250GeV/c photo-production no signal


0

1

2

3

3.4 4.1

Ent

ries

/ 4

MeV

/c2 Ξ

cc

+→D0pKπ

0

1

2

3

3.4 4.1

Ξcc

+→D0Λπ

0

1

2

3

3.4 4.1

Ξcc

++→D0Λππ

0

1

2

3

3.4 4.1

Ξcc

+→D0Λπππ

0

1

2

3

3.4 4.1

Ξcc

+→D0Ksp

0

1

2

3

3.4 4.1

Ξcc

++→D0Kspπ

0

1

2

3

3.4 4.1

Ent

ries

/ 4

MeV

/c2 Ξ

cc

+→D±pK

0

1

2

3

3.4 4.1

Ξcc

++→D±pKπ

0

1

2

3

3.4 4.1

Ξcc

++→D±Λπ

0

1

2

3

3.4 4.1

Ξcc

+→D±Λππ

0

1

2

3

3.4 4.1

Ξcc

++→D±Λπππ

0

1

2

3

3.4 4.1

Ξcc

++→D±Ksp

0

1

2

3

3.4 4.1

Ent

ries

/ 4

MeV

/c2 Ξ

cc

+→D±Kspπ

0

1

2

3

3.4 4.1

Ξcc

+→D±Λ

0

1

2

3

3.4 4.1

Ξcc

+→Λc±Kπ

0

1

2

3

3.4 4.1

M(Ξ_cc)GeV/c2

M(Ξ_cc)

Ξcc

++→Λc±Kππ

0

1

2

3

3.4 4.1

M(Ξ_cc)GeV/c2

M(Ξ_cc)

Ξcc

+→Λc±Kπππ

0

1

2

3

3.4 4.1

M(Ξ_cc)GeV/c2

M(Ξ_cc)

Ξcc

++→Λc±Ksπ

0

1

2

3

3.4 4.1

M(Ξ_cc)GeV/c2

Ent

ries

/ 4

MeV

/c2

M(Ξ_cc)

Ξcc

+→Λc±Ksππ

0

1

2

3

3.4 4.1

M(Ξ_cc)GeV/c2

M(Ξ_cc)

Ξcc

++→Λc±Ksπππ

0

1

2

3

3.4 4.1

M(Ξ_cc)GeV/c2

M(Ξ_cc)

Ξcc

+→Λc±Ks

M(Ξ_cc)

FOCUS Ξccsearch results


Why weakly decaying Doublet?

• Observed Excitation is ∼ 78MeV/c2:

• If Excitation is Chromomagnetic:

– Expect dominant M1 Dipole Transition (like in D? → Dγ)

– Weak decay of Chromomagnetic Excited State

Suppressed by ∼ 6 orders of magnitude

• Bardeen, Eichten and Hill: spectroscopy of cc compared to cs

(PRD68 054024, hep-ph/0305049)

Ground State: JP =1

2

+

[c ↑ c ↑ L = 0, JP = 1+] q ↓

Excited State: JP =1

2

−

[c ↑ c ↓ L = 1, JP = 1−] q ↓

• First excited state is L = 1 of heavy (cc) di-quark

• In at least one version of the model splitting is consistent with observed 78MeV/c2

• First EM transition is M2.


Charm Mysteries (1) – Discovery of the Ξ+c

CERN WA62 (1983)

• Beam: 135GeV/c Σ−

• 3 weeks of running

• no silicon detectors

• 83 events Ξ+c → ΛK−π+π+

• measured Ξ+c lifetime correctly


(Double)-Charm Mysteries (2) – J/Ψ ηc Production

• Belle observed high double charm pro-

duction in e+e− → J/Ψ cc, e+e− → J/Ψ ηc(Phys. Rev. Lett. 89 (2002) 142001, hep-ex/0205104)

• Belle does not see e+e− → J/Ψ J/Ψ (hep-

ex/0306015)

• At publication, factor x40 higher cross

section than theory.

• revised models still x10 too low.

• No confirmation from BaBar yet


Charm Mysteries (3) – Narrow Ds Resonances

BaBar, CLEO, Belle (2003)

D?sJ(2315)→ Dsπ

0, DsJ(2463)→ Dsγπ0

PRL90 (hep-ex/0304021); PRD68;

PRL91 (hep-ex/0308019)


SELEX Search: η Signal in Charm trigger

SELEX Photon detection (Leadclass):

• Energy scale verified on π0, Σ0:

Good to < 2% over full energy range

• Also on D∗.

η → γγ

• Eγ > 2GeV

• Eγγ > 15GeV

• Good fit to: exponential + Gauss

– Fit M(η) = 544.9± 2.9

– PDG M(η) = 547.3± 0.12

– Fit Width: 27.8± 4.3

– MC resolution: 30.2± 1.2

10 4

450 475 500 525 550 575 600 625 650 675 700

MeV/c2

even

ts /

4 (M

eV/c

2 )mη 544.8 ± 2.9

M(γγ)

450 550 650-100

0

100

200

300

400

500

η-yield per interaction: 0.05


SELEX Search: Ds Signal in Charm trigger

Ds → K−K+π−


SELEX: D?sJ(2632) → D+

s η

• Combine Ds events with η candidates

• Reject events withNη > 5 (loss: 18/554)

• Background: mix η from 25 other events

with each Ds and rescale

• 43.4± 9.1 signal events for Gaussian fit

to substracted data; χ2 = 0.9

• 6.2σ peak at 2635.4MeV/c2

η-yield:

• in signal band: 0.18 per interaction with

Ds

• Remove Signal: .12± 0.05

0

2.5

5

7.5

10

12.5

15

17.5

20

22.5

600 800 1000 1200 1400MeV/c2

even

ts /

10 (

MeV

/c2 )

∆M = M(K+K-π+ η) - M(K+K-π+)

Mass 2635.4 ± 3.2Ds+ η

550 650 750 850 950-5

0

5

10

15

hep-ex/0406045, submitted to PRLRecent SELEX results on the properties of charmed hadrons Jurgen@QC2004 22Sep2004. 27

SELEX: D?sJ(2632) → D0K+

500 550 600 650 700 750 800 850 900∆M = M(K-π+K+) - M(K-π+)

0

2

4

6

80

2

4

6

8

MeV/c2

even

ts /

5 (M

eV/c

2 )

Mass 2569.9±4.3 2631.5±1.9

b) D0 K-

a) D0 K+

Γ(D0K+)

Γ(D+s η)

= 0.16± 0.06

• Well identified D0, K+

– D0 → K−π+ only (S/N 4/1)

– Prob(K+) > 10 Prob(any other)

• Wrong sign background constant

• Fit to 2 Breit-Wigner with Gaussians,

and constant background

• Width of Gaussians fixed from MC

DsJ(2573) Mass Width Γ

PDG 2573± 1.7 15+5−4SELEX 2569± 4.3 14+9−6

14± 4.5 Events at 2631.5± 1.9MeV/c2

Poisson excess prob. 10−4

90% CL upper limit: Γ < 17MeV/c2

ABOVE THRESHOLD!WHYNARROW?


Look at Ds(2112) → Dsγ

0

20

40

60

80

100

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

Σ- Beam: Dsγ

mass difference:

143.7(1.4) MeV/c2

S+B: 221 events

B: 160 events

significance: 4.8 σ

(M(Dsγ)-M(Ds)) GeV/c2

Eve

nts

/.01

GeV

/c2

-10

0

10

20

30

40

50

60

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

Σ- Beam: Dsγ

background-subtractedmass difference:145.6(2.0) MeV/c2

yield: 60.1 eventsχ2/Ndof = 0.94

(M(Dsγ)-M(Ds)) GeV/c2

Eve

nts

/.01

GeV

/c2

• CLEO:Ds(2112)/Ds: 0.59± 0.03± 0.01

• SELEX: Ds(2112)/Ds: 0.24± 0.06

• BUT: A lot of Ds come from Ds(2632) !

Corrected SELEX Yield:

Ds(2112)/Ds: 0.53± 0.13

• Ds(2632) has different production mech-

anism

• What is it?


Summary and Outlook

• SELEX observes the Ξ+cc(3520) in two

decay modes: Ξ+cc → Λ+cK−π+,

Ξ+cc → pD+K−

• SELEX observes two doublet of weakly

decaying Double Charm Baryons:

– Ξ+cc (3443)→ Λ+cK−π+

Ξ+cc (3520)→ Λ+cK−π+

– Ξ++cc (3460)→ Λ+cK−π+π+

Ξ++cc (3541)→ Λ+cK−π+π+

– Isospin splitting ∼ 19MeV/c2

– Excitation ∼ 78MeV/c2

– decay of lower states compatible with

phase space, higher states not

• SELEX observes an excited Double Charm

Baryon: Ξ?++cc → Ξ+cc π

+

• Double Charm Baryons produced

by baryons (Σ−, p)

• Lifetime at resolution limit: τcc < 30 fs

• SELEX is working on other decay modes:

– Most promising Ξ+(+)cc → Ξ+c π+π−(π+)

– Eventually also go to the Ω++cc

• SELEX observes new excited Ds Meson

in two decay modes: DsJ(2632)→ D+s η

andD0K+, with small width, and mostly

decaying to D+s η

• SELEX is working on charmed baryon

properties:

– Ωc lifetime

– Ξc lifetimes

– D±, D0 production


Documents

RecentSELEXResultsonthePropertiesofCharmedHadrons · 4 6 8 10 12 14 0 50 100 150 200 250 300 Momentum [GeV/c] Radius [cm] SELEX RICH 53229793 Single negative track events Omega Xi